Investigating the Impacts of Building HVAC Systems on Aerosol Composition and Concentration

XINXIU TIAN, Bryan Berman, Bryan Cummings, Shannon Capps, Michael Waring, Peter F. DeCarlo, Johns Hopkins University

     Abstract Number: 265
     Working Group: Indoor Aerosols

Abstract
This work investigates how aerosols change in concentration and composition as they move through heating, ventilating, and air-conditioning (HVAC) systems. Without strong indoor emissions, outdoor-originated aerosols are the main contributor to indoor aerosols. Upon transport to the indoor environment through building HVAC systems, outdoor aerosol concentrations and chemical compositions are modified due to filtration and air conditioning (heating or cooling), especially when the indoor-outdoor temperature gradient is significant. Measurements were conducted in a modern HVAC system on the Johns Hopkins University Campus in Baltimore, MD. During the measurement period, the instrumentation sampled air from a valve switching system pulling from four different zones inside of the HVAC system: 1) return air, 2) mixed air where outdoor air is mixed with returned indoor air, 3) post filter and heating coil, and 4) supply - post cooling coil. We used a variety of instruments to measure the concentration and chemical composition of particulate matter and gases and T/RH. Instrumentation included 1) Soot Particle Aerosol Mass Spectrometer (SP-AMS), 2) scanning mobility particle sizer (SMPS), 3) proton transfer reaction – mass spectrometry (PTR-MS), 4) Three PICARRO gas concentration analyzers measuring CH₄, CO, CH₂O, CO₂, NH₃, and 5) Quant-AQ MODULAIR-PM. Results from this study demonstrate that the primary source of PM in the building originates outdoors. Positive Matrix Factorization on the organic component of the aerosol indicated 4 different sources. The identified factors changed in relative concentration as they passed through the HVAC system. The results also suggest that the filtration efficiency of the MERV filters in the HVAC varied for different species, and the installed filters did not achieve the expected filtration levels.